Contained Materials - std301320040047

DOE-STD-3013-2004

any benefits, does not pose any new problems, and does allow correction of an

anachronism in the current criteria.

A.6.3

Contained Materials

A.6.3.1

Container Fill Gas

1. The stored material condition should not change significantly because of reactions

with the container atmosphere. If material stabilization has to be repeated, there

would be additional handling and unnecessary worker radiation exposure.

2. The container atmosphere must not act to mask leak testing and must support leak

testing.

A.6.3.2

Mass of Contained Materials

1. The mass limit for fissile materials is based on criticality safety limits for plutonium.

239

Pu that is fully water-reflected and

The fissile mass of an isolated sphere of pure

has a 0.05 margin in keff is calculated to be 4.53 kg (9.98 lb.). The parameter keff

indicates the criticality status of an assembly of fissile and possibly other materials

a value of 1.0 indicates the critical condition (a self-sustaining reaction) and values

less than 1.0 indicate subcriticality, with smaller values signifying greater departures

from criticality. A margin of 0.05 (a keff of 0.95) is commonly used to assure

subcriticality. In other words, the smallest amount of plutonium that could go critical

is somewhat more than 4.53 kg. The 4.4 kg limit specified corresponds to the limit

for some shipping packages and allows a modest additional margin of safety. Note

239

Pu. This constraint

that the mass limit applies to all fissile species and not just

233

235

prevents potential criticality incidents involving stored fissile materials (i.e.,

237

Np, or higher plutonium isotopes) because the critical masses of these fissile

239

Pu.

radioisotopes are greater than that of

In terms of plutonium mass, 5.00 kg (11.02 lb.) of plutonium oxide is equivalent to

4.40 kg (9.70 lb.) of plutonium metal. The oxide weight limit refers to the total mass

of the plutonium-bearing materials present, not just to the plutonium oxide content.

This constraint provides additional assurance of subcriticality by making the

conservative assumption that all the contents are pure plutonium dioxide. Mass limits

may be further limited by facility-specific considerations including administrative